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- Radiometric Dating
And let me be very clear. Let's look at the periodic table over here. So carbon by definition has six protons, but the typical isotope, the most common isotope of carbon is carbon So carbon is the most common. So most of the carbon in your body is carbon But what's interesting is that a small fraction of carbon forms, and then this carbon can then also combine with oxygen to form carbon dioxide. And then that carbon dioxide gets absorbed into the rest of the atmosphere, into our oceans.
It can be fixed by plants. When people talk about carbon fixation, they're really talking about using mainly light energy from the sun to take gaseous carbon and turn it into actual kind of organic tissue. And so this carbon, it's constantly being formed. It makes its way into oceans-- it's already in the air, but it completely mixes through the whole atmosphere-- and the air. And then it makes its way into plants. And plants are really just made out of that fixed carbon, that carbon that was taken in gaseous form and put into, I guess you could say, into kind of a solid form, put it into a living form.
That's what wood pretty much is. It gets put into plants, and then it gets put into the things that eat the plants.
So that could be us. Now why is this even interesting? I've just explained a mechanism where some of our body, even though carbon is the most common isotope, some of our body, while we're living, gets made up of this carbon thing. Well, the interesting thing is the only time you can take in this carbon is while you're alive, while you're eating new things.
Because as soon as you die and you get buried under the ground, there's no way for the carbon to become part of your tissue anymore because you're not eating anything with new carbon And what's interesting here is once you die, you're not going to get any new carbon And that carbon that you did have at you're death is going to decay via beta decay-- and we learned about this-- back into nitrogen So kind of this process reverses.
So it'll decay back into nitrogen, and in beta decay you emit an electron and an electron anti-neutrino. I won't go into the details of that. But essentially what you have happening here is you have one of the neutrons is turning into a proton and emitting this stuff in the process. Now why is this interesting?
Carbon 14 dating 1 (video) | Khan Academy
So I just said while you're living you have kind of straight-up carbon And carbon is constantly doing this decay thing. But what's interesting is as soon as you die and you're not ingesting anymore plants, or breathing from the atmosphere if you are a plant, or fixing from the atmosphere. And this even applies to plants. Once a plant dies, it's no longer taking in carbon dioxide from the atmosphere and turning it into new tissue. The carbon in that tissue gets frozen. And this carbon does this decay at a specific rate. And then you can use that rate to actually determine how long ago that thing must've died.
So the rate at which this happens, so the rate of carbon decay, is essentially half disappears, half gone, in roughly 5, years. And this is actually called a half life. And we talk about in other videos. This is called a half life. And I want to be clear here. You don't know which half of it's gone. It's a probabilistic thing. You can't just say all the carbon's on the left are going to decay and all the carbon's on the right aren't going to decay in that 5, years.
So over the course of 5, years, roughly half of them will have decayed. Now why is that interesting? Well, if you know that all living things have a certain proportion of carbon in their tissue, as kind of part of what makes them up, and then if you were to find some bone-- let's just say find some bone right here that you dig it up on some type of archaeology dig.
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And you say, hey, that bone has one half the carbon of all the living things that you see right now. It would be a pretty reasonable estimate to say, well, that thing must be 5, years old.
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Even better, maybe you dig a little deeper, and you find another bone. Maybe a couple of feet even deeper. So how old is this? And then after another half life, half of that also turns into a nitrogen And so this would involve two half lives, which is the same thing as 2 times 5, years. Or you would say that this thing is what? You'd say this thing is 11, years old, give or take. They will use the evidence from the activity to make inferences about what the Earth was like during the time the fossils existed. Students will develop an understanding of how fossils give scientists clues as to what the early Earth was like in the past.
Students will also show how fossils can be used to relatively date rock layers using the Law of Superposition and index fossils. This lesson is meant to illustrate how we can use these layers to discover the relative age of an object found in that layer by utilizing the Law of Superposition. This is the first lesson in a unit of 4 lessons that integrates science, math, and computer science standards to teach the concept of half-lives and radioactive dating. This is Lesson 2 in the Radioactive Dating Unit and will begin the experience in coding a program to illustrate student understanding of radioactive dating.
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This is the final lesson in the Radioactive Dating Unit. This decision requires an understanding of the concept of a half-life and the benefits and limitations of radiometric dating. Students must complete mathematical calculations involving equations and operations with fractions and percentages. Students completing this MEA must develop two essays that respond in a professional manner to a client in the scientific industry. Students will investigate the correlation between rock layers and fossil age.
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Students will also become familiar with the Law of Superposition and apply to finding the relative age of excavated "fossils". At the conclusion of this lesson, students will understand the term half-life and know how to utilize a graph of radioactive decay to approximate the age of a "fossil". This activity involves recording and graphing data as well as a short data analysis segment. Measuring the Age of the Earth: Students will build a timeline based on the masses of substances to develop a basic understanding of absolute age by radioactive dating and how it compares to relative age based on the Law of Superposition.
Students will measure the mass of several objects which will represent "fossils.
Students will gain an understanding of how scientists use absolute dating to accurately determine the age of objects and how relative dating is used to generally determine the age of objects. This tutorial is designed to help secondary science teachers learn how to integrate literacy skills into their science curriculum.
This tutorial will demonstrate a number of strategies teachers can impart to students to help them use context clues to determine the meaning of unfamiliar words within science texts. It will also help them teach students how to select the appropriate definition from reference materials. The focus on literacy across content areas is intended to help foster students' reading, writing, and thinking skills in multiple disciplines.